The invention relates to a new process and apparatus for the recovery of cellulose fibres or other non-plastic material and plastics from plastic-coated fibrous cellulose materials, plastic-coated metal foils, or the like.
The increased use of plastic-coated papers, metal foils, and/or boards constitutes a large source of waste, from which plastic and a high quality cellulosic material, metal foil, or the like can be recovered.
This waste material cannot easily be recovered by conventional wet-pulping methods. Furthermore, the plastic material, which constitutes a quite large and the most expensive portion of the waste material, must be recuperated free of fibres to enable its reuse. This is a very important for economic reasons, since otherwise the problem of disposal of these material will become quite serious.
In the term "plastic material", I include the polyolephinic resins, such as polyethylene, the polyvinyl chloride resins, the polyester resins, the plastic-aluminium foil laminates and other films which can be laminated or extruded on papers and boards.
The known methods for the recovery of such plastic-treated cellulosic materials are mainly based either on the dissolution of the plastic materials by chemical solvents, or on the mechanical separation of the cellulosic fibres from plastics, in water suspension. In those methods, based on the solvent extraction, the chemical solvent only removes the plastics, while the papers and boards remain unaltered and must be further wet-pulped to be transformed in fibers.
The solvent-extraction processes have considerable drawbacks: they are two-stage processes and the high chemical solvent losses have an important economic influence on the final cost of the recovered fibers.
Processes based on the mechanical separation of the cellulosic portion from the plastic-coated cellulosic materials are described in the U.S. Pat. No. 3,339,851 and in the corresponding British Patent No. 1,020,003 assigned to the Black Clawson Co., and in the French Patent No. 1,407,574 assigned to the Amberley Corp.
U.S. Pat. No. 3,339,851 only claims a wet-pulping apparatus. In the description of the above mentioned patent and in the British Patent No. 1,020,003 claims, a method for treating plastic-coated waste paper materials is presented.
The waste material is pulped in a water suspension, in a special tub, which is claimed in both patents, in order to obtain the separation of the fibrous material from the plastics; water is added continuously in the tub, loading the tub with additional waste material, while continuously removing liquid and fibrous material through a perforated screen situated on the bottom of the tub, and removing the plastics through a junk-remover.
This method can also be performed as a batch operation (this is the method which is used in actual practice and which is described in the Black Clawson bulletins "A guide to Waste Paper Utilisation;" by W. A. Banks, and in the "Polypulp and Polisolv Bulletin").
In that case, after pulping for sufficient time, the tub is emptied, again filled with water and re-emptied several times.
The plastics left in the tub is removed by any suitable means, for ex. by hand, or fork, or by an apparatus such as is shown in British Patent No. 713,501.
The main drawback of the process described in the first two above-mentioned patents is the impossibility to realise, in practice, continuous operation, as can be seen in all the industrial plants based on the Black-Clawson patents. It is in fact impossible to remove continuously the plastic material from the tub in which the separation of the cellulosic fibre material from the plastics has been effected, because a certain pulping time is necessary to achieve the mechanical separation. between the plastics and the fibrous material. If the plastics is removed continuously, some of the added waste paper material would be removed as plastic-coated paper.
The main drawbacks of batch-operation on the basis of the Black-Clawson method are: loss of time in refilling the tub with water several times, in order to remove the major portion of the fibres through the bottom screen; a large capacity tub (approximately 36 cubic meters) is required; the plastics in the tub is contaminated by a large portion of fibres; the plastic material, when it exceeds 20% of the fibres in the water suspension, tends to block the screen perforations.
Furthermore, the rotor, claimed in the above mentioned two patents, has the tendency to reduce the plastic to small fragments which contaminate the cellulose so that fine and expensive cleaning and screening are necessary.
In French Patent No. 1,407,574 is described quite a similar batch-operation method for the recovery of cellulosic fibres from plastic-coated cellulosic material. In this case also, the separation of the cellulosic fibres from plastics is performed in the pulping apparatus, by adding water in order to maintain a certain level, while the liquid and fibres are removed through a perforated screen situated on the bottom of the pulping apparatus. Fine cleaning is necessary to separate the small plastic fragments from the fibres. The plastics left in the pulping apparatus is removed by a non-described method.
This method has all the drawbacks of the Black Clawson method, as above described.